Method for operating rotating cylindrical filters and a rotatable cylindrical filter

ABSTRACT

A method for application in conjunction primarily with so-called rotating filters of the kind which include a substantially cylindrical filter tube (1) which is provided with a permeable wall and which is sealingly journalled at preferably two axially spaced locations, preferably at the ends of the tube, and which is arranged for rotation about its longitudinal axis in a filter jacket (2), wherewith material to be filtered, the so-called feed, is supplied to a space or chamber (11) located between the filter jacket and the filter tube, and the filtered substance, the filtrate, being tapped-off from the interior of the filter tube. 
     The method is particularly characterized by sealing and journalling the filter tube (1) in a manner adapted to substantial changes in temperature in the filter tube and that facilities are provided for sterilizing the filter. When applicable, the bearings and seals can be sterilized and lubricated and cooled by means of sterilizing media, and, when applicable, the filter tube (1) is caused to rotate at relatively high speeds. 
     The invention also relates to a device for carrying out the method.

The present invention relates to a method in rotating filters of thekind which include a substantially cylindrical filter which has apermeable tube wall and which is journalled sealingly at preferably twoaxially spaced locations, preferably at the ends of the tube, forrotation about its longitudinal axis in a filter jacket, in which methodmaterial to be filtered, the feed, is fed to a space between the filterjacket and the filter tube, and in which the filtered material,hereinafter called the filtrate, can be removed from the interior of thefilter tube.

The invention also relates primarily to a so-called rotating filter forcarrying out the method.

Methods and filters of essentially the aforementioned kind are known tothe art. The prior art techniques, however, are encumbered with suchdrawbacks as high costs, relatively limited capacities with regard,e.g.,to the dry solids contents that can be achieved therewith, and therelatively small possibility of maintaining flexibility with regard toconditions of use and maintenance and the fulfillment of high sterilerequirements.

The present invention provides a method and filter which are notencumbered with such drawbacks. Thus, the cost of each unit of filtrateis low. Moreover, the invention enables beneficially high rotationalspeeds to be used. Flexibility with regard to use is also high. Themethod and filter according to the invention are particularly suited foruse in biotechnical applications where demands on sterility are high.The word sterilization is used here as a common designation forprocesses which are intended to reduce or eliminate the risk ofspreading infection. It will be understood that the invention alsopertains to such processes as pasteurization and the like. Therotational motion is utilized, inter alia, to increase capacity and toimprove journal and sealing functions.

Thus, the invention relates to a method for application in conjunctionwith primarily so-called rotating filters of the kind in which thefilter includes a substantially cylindrical filter tube which has apermeable tube wall and which is sealingly journalled at preferably twomutually spaced axial locations, preferably at the tube ends, forrotation about its longitudinal axis in a filter jacket; in whichmaterial to be filtered, the feed, is fed to a space between the filterjacket and the filter tube; and in which filtered material, thefiltrate, can be tapped from the interior of the filter tube.

The method is particularly characterized by sealing and journalling thefilter tube in a manner adapted to substantial temperature changes ofthe filter tube and in a sterilizible or like manner; by sterilizing andlubricating and cooling bearings and seals when applicable with the aidof sterilizing media; and by rotating the filter tube, when applicable,preferably at a relatively high speed.

The invention also relates to a filter of primarily the socalledrotating kind which includes a substantially cylindrical filter tubewhich has a permeable tube wall and which is journalled at preferablytwo axially spaced locations, preferably at the ends of the tube, forrotation about its longitudinal axis in a filter jacket; and with whichfilter material to be filtered, so-called feed, is intended to be fed toa space between the filter jacket and the filter tube, and the filteredmaterial, the filtrate, is intended to be tapped from the interior ofthe filter tube.

The filter is particularly characterized in that seals and bearings arearranged to take-up axial displacement movements and forces caused andcreated by substantial temperature changes in the filter tube; in thatmeans are provided for sterilizing or similarly treating the filtertube; in that means are provided for sterilizing and for lubricating andcooling bearings and seals when applicable; and in that the filter tubeis arranged for rotation at relatively high speeds.

The invention will now be described in more detail with reference toexemplifying embodiments thereof and to the accompanying drawings; inwhich

FIG. 1 illustrates schematically and partially in axial section a firstembodiment of a filter constructed in accordance with the invention;

FIG. 2 is an enlarged view of the right-hand part of FIG. 1;

FIG. 3 illustrates schematically a second embodiment of end journalmeans intended for the same purpose as in the FIG. 2 embodiment and seenas in FIG. 2;

FIG. 4 is a schematic illustration of the filter shown in FIG. 1, seenfrom the right in said Figure;

FIG. 5 illustrates schematically an embodiment of end journal meansprovided with a pump impeller, essentially in accordance, e.g., withFIG. 2 and seen as in FIG. 2;

FIG. 5a illustrates schematically a centrifugal pump impeller for usessentially in accordance with FIG. 5;

FIG. 6 illustrates schematically a third embodiment of end journal meansseen as in FIG. 2;

FIG. 7 illustrates schematically and in axial section a filter whichcomprises a conical filter jacket;

FIG. 8a illustrates schematically and in axial section a filter havingan internal suction box for back flushing, an end view being shown inFIG. 8b;

FIG. 9a illustrates schematically and in axial section a filter having aback flushing section box, an end view being illustrated in FIG. 9b; and

FIG. 10 illustrates schematically a fourth embodiment of end journalmeans seen as in FIG. 2.

In FIG. 1 the reference 1 identifies a substantially cylindrical filtertube which is provided with a liquid permeable wall and which in theillustrated embodiment is sealingly journalled at two axially separatedlocations, in this case at the tube ends. The tube is journalled forrotation about its longitudinal axis in a filter jacket 2. In theillustrated embodiment, the filter jacket 2 is sealingly attached bymeans of flanges 2' at two end-cover parts 3', 3", sealing rings 4 beingprovided peripherally between the flanges 2' and the end-cover parts 3',3". The one endcover part 3' forms an attachment for a drive means, e.g.an electric motor 5 by means of which the filter tube 1 is rotated via ajournal and sealing unit. The filter tube of this embodiment isconnected to a shaft 6 to which torque is transmitted via a resilientcoupling 7 and which is journalled by means of ball bearings 8. Theshaft 6 is passed sealingly through the end-cover 3', the seal of theillustrated embodiment being a double, mechanical plain seal 9: Locatedbetween the substantially large sealing surfaces of the double seal 9 isa space 10 to which a cooling and lubricating medium is supplied throughchannels not shown. The journalling and sealing unit is sterilized bymeans of heat, e.g. by means of steam, via, inter alia, the space 10.

The space 11 located between the filter tube 1 and the filter jacket 2is intended to receive material to be filtered, socalled feed.Subsequent to passage through the wall 1 of the filter tube, thefiltrate is tapped from the interior 12 of the tube. The space 11 can beplaced under pressure to this end.

The other end-cover part 3" carries attachment means for attachment ofthe end 1' of the tube 1 remote from the drive motor. The tube 1 issealingly journalled to a non-rotatable shaft 13, which is connected tothe end-cover 3" and journalled for movement in the direction of thelongitudinal axis of the shaft while maintaining the shaft sealed. Theembodiment illustrated in FIG. 1 is provided to this end with ajournalling and sealing unit which comprises a double, mechanical plainseal 14 and includes a first part 15 which is sealingly journalled tothe shaft 13 and includes an external, substantially cylindrical part15', and further includes a second part 16 which is sealingly connectedto the filter tube 1 and, when seen in the direction of the tube radius,is arranged essentially between the filter tube and said first part andincludes an internal, substantially cylindrical part 16' which is sealedand axially displaceable in co-action with the external cylindrical part15' of the first part 15, the filter tube 1 at said end 1' beingsealingly fitted to said non-rotatable shaft 13. The reference 17identifies sealing means intended for cooperation in said co-action. Inthe FIG. 1 embodiment the journal means comprises two ball bearings 18.The reference 19 in FIGS. 1 and 2 identifies an impeller or like devicewhich is intended to rotate with the filter tube about said axialdirection and is herewith arranged in an existing cooling andlubricating system for cooling and lubricating the bearings of thejournalling and sealing unit, and is herewith arranged to circulatecoolant and lubricant for, inter alia, temperature equalizing purposes.The impeller 19 may be constructed in a number of ways, for example, mayhave a T-shaped cross-sectional profile as illustrated in FIG. 1,including grooves in the flange-like part facing the shaft 13, saidgrooves forming a given angle to said longitudinal axis.

In the FIG. 3 embodiment, the said first part 15 of the journalling andsealing unit for the tube end 1' is arranged between axially sprungsealing devices 21, via sealing surfaces 20. The two parts 15, 16 ofthis embodiment also include substantially cylindrical parts 15', 16'.

According to one preferred embodiment, the aforesaid nonrotatable shaftis provided with at least one axially extending channel 22, FIG. 4,which connects the interior 12 of the filter tube 1 with the outersurroundings of the filter jacket. Thus, there is conveniently provideda channel 22 through which the filtrate can be tapped-off. Suitably amultiple of channels are provided, in FIG. 4 illustrated as outletopenings in a connecting piece 23 arranged adjacent the shaft 13, suchas a further channel 22, e.g., for supplying flushing and washing liquidand/or gas such as an inert shielding gas, to the interior of the filtertube, and channels 22', e.g., for measuring pressure, circulatingcoolant and lubricant for bearings, seals etc.

In accordance with preferred embodiments the filter tube 1 has providedtherein scavenger pipes, scavenger plates or the like for removal offiltrate from the interior 12 of the filter tube as the filter rotates,said rotational movement in the correct direction being capable ofgenerating feed pressure. An embodiment which incorporates a scavengerpipe or tube 24 is illustrated schematically in FIGS. 1, 2 and 4. Whenusing scavenger plates, not shown, there is employed an impellerprinciple in which the impeller/plate is stationary and the liquid isimparted a rotational movement and is fed towards the centre of theimpeller/plate. In the illustrated embodiment, in which the scavengerpipe 24 extends through the shaft 13, the discharge of filtrate can beadjusted by means of the pipe 24, which includes a part 24' whichextends substantially in the direction of the longitudinal pipe axis anda further part 24" which is connected to said part 24' and extends atleast partially radially in the filter tube (1), said further part 24"incorporating at its free end 25 a filtrate inlet 26 which facessubstantially tangentially in the filter tube and in which said axiallyextending part 24' is eccentrically located in the filter tube, so thatthe radial position in the filter tube of the filtrate inlet 26 adjacentsaid free end 25 can be adjusted by rotating the axially extending partabout the longitudinal axis of said part, thereby displacing the inlet26 in towards a plane extending essentially at right angles to saidlongitudinal axis, by pivoting the radially extending part 24" about aneccentrically located longitudinal axis. A scavenger plate can beadjustably arranged in an essentially corresponding manner, by arrangingfor the diameter of the vane-plane of the plate or the like to bevaried. The scavenger pipe of the illustrated embodiment is rotatable inthe shaft 13 and protrudes therefrom and terminates in a knob or handle13" and can be locked against rotation by means of a clamping device 27or the like. According to one preferred embodiment, an impeller 28 orthe like, FIGS. 2 and 5, is arranged at the end of the filter tube 1journalled for axial displacement, and is capable of being rotated aboutsaid longitudinal axis by means of the tube 1, the impeller or the likebeing intended to lower the pressure in central parts so as to relievethe pressure, either totally or partially, in the location of the seal14 in the filter jacket. The impeller 28 is preferably a centrifuge-typeimpeller, although other kinds of impeller can be used of course. Animpeller 28 is illustrated highly schematically in FIGS. 2 and 5. FIG.5a is a view of an impeller seen in the direction of its long axis andprovided with vanes 28' or the like.

Preferably the aforesaid impeller 28 or like device is also providedwith vanes 29 or the like for advancing material axially in the filterjacket, such as the discharge of sludge or slime. When the vanes 28' and29 are intended for similar feed functions the feed is effectedsubsequent to reversing the impeller, i.e. changing the direction ofrotation. The reference 30 identifies fastener screws for an impeller28, which are shown arranged in a part 16 by way of example.

Preferably, the filter jacket has arranged therein adjacent the inletend of the tube 1 an impeller 31 or the like, referenced in FIG. 1, i.e.adjacent the existing inlet 32 for material to be filtered, thisimpeller 31 or the like being intended to increase the pressure at saidinlet so as to improve the feed of said material into the filter jacket2 (i.e. the flow of the unfiltered liquid both along the filter tube andin a direction tangentially thereto), and preferably for relieving,either totally or partially, the pressure prevailing in the vicinity ofthe journalling and sealing unit located adjacent said inlet in thefilter jacket, in this case that part of the plain seal 9 locatednearest the filter tube In this case, the impeller may, e.g., be of thecentrifuge type, and may also be arranged for axial feed in a directionaway from the inlet 32. The reference 33 identifies an attachment in theend-cover of the tube 1 for an impeller 31.

In the embodiment illustrated in FIG. 6 journalling is effected with theaid of slide bearings. The aforementioned parts 15 and 16 are arrangedessentially in the manner described with reference to FIG. 1. The parts15 and 16 of this embodiment are connected by means of a locking pinwhich prevents relative rotation between the locking parts 15 and 16.The locking pin 34 is constructed such that the tube 1 is journalled foraxial movement in the aforedescribed manner. The plain seals illustratedsymbolically in FIG. 6 can take-up a part of the aforesaid displacementmovement. The construction of plain seals 20, 21 which are capable oftaking-up such axial displacement is illustrated in FIG. 3.

The reference 35 in FIG. 3 identifies a scavenger pipe for completescavenging of the filter tube, where the filter is intended to be usedin a position in which its longitudinal axis extends substantiallyvertically, not shown in FIG. 3, there being arranged in the tube 1 asimilar space 36 in the vicinity of the lower end of the tube, thisspace being the last region to be rendered dry when emptying the filtertube, where the inlet opening 35' of the scavenger pipe 35 is located inthe bottom part of the space 36 in order to enable the filter tube to bescavenged to a substantially dry state, the inlet opening of thescavenger pipe preferably having a small dimension and suitably combinedwith a scavenger pipe of standard dimensions.

The space 11 may have arranged therein one or more baffles, not shown,for creating turbulence and vigorous agitation in said space. Eachbaffle forms a gap with the filter tube, this gap being narrower thanthe radial distance between the filter tube and the filter jacket. Theuse of baffles enables the turbulence in the space 11 to be increased,with subsequent increase in the capacity of the filter. A correspondingeffect can be obtained by decreasing the distance between the filtertube 1 and the filter jacket 2. This will also reduce the volume ofunfiltered liquid.

The filter jacket 2 of the filter embodiment illustrated in FIG. 7 has aconical configuration, and therewith widens outwardly towards the end 2'at which the sludge or slime outlet is located and from where saidsludge or slime is removed. This filter jacket configuration facilitatessludge discharge.

The method according to the invention and also the manner in which thefilter according to the invention operates will be apparent in allessentials from the aforegoing. Thus, the material to be treated is fedthrough an inlet 32 to the space 11 located between the filter tube andthe filter jacket, there being maintained in said space a pressure whichdeviates from the pressure prevailing in the filter tube. The filtrateentering the space 11 passes through the wall of the tube 1 under theinfluence of an overpressure relative to the pressure in the filtertube. A given variable through flow of material is maintained in thespace 11, and a concentrate outlet 32' is preferably provided at the endof the filter opposite said inlet end. The filter tube is rotated at asuitable speed. The axially displaceable journal means enables a sealedjournal to be maintained even when substantial changes in temperatureetc. occur. The journal means, which can be sterilized, thus satisfy thehigh requirements placed on such seals and, when appropriate, thejournals and seals are sterilized and lubricated and cooled by means ofa sterilizing agent, such as steam.

So-called back flushing or back washing, i.e. the passage of, e.g.,filtrate through the wall of the filter tube from the interior 12 of thetube 1 out to the space 11 between the tube 1 and the filter jacket 2,can be achieved through suitable facilities and is effected for thepurpose of, inter alia, cleansing the active part of the filter and forremoving unsuitable coatings, impurities, etc. liable to lower capacity,and, when appropriate, to cooperate in creating an effective filteringlayer or cake on the filter tube 1, such a cake being referred to as aso-called dynamic membrane. Back flushing can be effected by changingthe pressure in the filter unit so as to decrease the pressuredifferential available for filtering across the filter, i.e. primarilythe pressure differential between the spaces 11 and 12, the pressure inthe space or chamber 11 being greater than the pressure in the space orchamber 12. When this pressure differential is decreased sufficiently,filtered liquid is forced by centrifugal force back through the wall ofthe rotating filter tube and into the space 11. The back flushing thuseffected flushes away particles and/or loosens particles which wouldotherwise tend to block the filter and therewith lower the filteringcapacity. Back flushing can be achieved at a given, relatively lowpressure difference, by increasing the rotational speed of the tube 1.Furthermore, as the filter tube 1 rotates, and also the liquid forcedthrough the tube 1 by back flushing, together with the liquid locatedexternally of the tube, those particles which are nominally heavier thanthe medium, which may be liquid and/or gas, surrounding the tube 1 arepropelled outwards in a direction towards the cylindrical surface of thefilter jacket 2. The pressure differential can also be reduced bydecreasing the pressure on the incoming material to be filtered and/oron the outgoing unfiltered material, i.e. the concentrate, or byincreasing the pressure and/or the quantity in the filter tube, i.e. thepressure in the space or chamber 12. This increase can be effected bysupplying gas and/or liquid under suitable pressure through e.g., aflushing or washing pipe 22. Back flushing can also be effected byconnecting the interior of the filter tube or the outer cylindricalsurface thereof to a "suction box" 45. In the FIG. 8 embodiment thesuction box is arranged against the inner cylindrical surface of thetube 1, and against the outer surface in the FIG. 9 embodiment. Backflushing is effected once with each turn of the tube wall in each case.When scavenging pipes, scavenging plates or like devices are used, theamount of liquid available for back flushing purposes can be varied,inter alia, by adjusting the rotational position of the tube or byadjusting the diameter of the scavenging plate and therewith the amountof liquid in the filter tube. It will be understood, however, that theamount of available liquid can also be varied in other ways, e.g. bycreating back pressure, rotational changes, etc., and also through theamount of filtrate in scavenger pipes etc. and connecting systems.

The filter is preferably sterilized with the aid of pressurized steam,which is introduced through the inlet 32. Steam, sterile hot oil, or thelike, is also passed through the seals 9, 14 etc., the spaces 9', 1013', 14' etc., forming part of the cooling and lubricating system beingused to this end. In this regard a given overpressure is maintained inthe sealing system filled with sterile medium, in order to prevent theunintentional ingress of undesirable media. For the purpose of avoidingunderpressure, sterile medium, such as air or water, must be supplied,particularly when cooling the filter unit.

FIG. 3 illustrates an embodiment in which cooling and lubricatingliquid, such as water, is supplied to one side of the journal means, asindicated by the arrows 20, and removed at the other side in a systemwhich, by flushing clean at an overpressure, holds the bearing meansshielded from the filtrate and concentrate, thereby avoiding, e.g.,taste impairments as a result of oil impurities in the filtrate. Anarrangement essentially according to FIG. 3, in which the spaces arelocated, e.g., on both sides of the ball bearing 21', means and spacescan be arranged for, with the aid of a suitable medium, preferably whenwashing and/or sterilizing, heating the journal means for the purpose ofde-watering lubricating grease. Means and spaces can also be providedfor subjecting the bearing means to an underpressure for the purposede-watering lubricating grease.

The filter is particularly constructed and suitable for forming andutilizing an additional filtering membrane in addition to the filtertube, with an external coating of filter fabric, filter net, or filtermembrane of a kind suitable for the process concerned with regard topermeability (mesh size, pore size, etc.), sensivity to temperature andchemicals (sterilization etc.), etc. Dynamic membranes can be formedwith the aid of filter auxiliaries which can be supplied in variousways, e.g. with sterilizing medium, filtrate or feed, and maybe ofvarying kind, such variables as particle size, particle form, density,etc. being of significance. Filter auxiliaries, which may also comprisea constituent of the material to be filtered, can be fractionated intosuitable fractions and orientated, by utilizing the rotational movementand varying the speed and/or direction of said movement and/or varyingthe flow direction of the material to be filtered, i.e. the through flowof material and/or the aforesaid back flushing. Unsuitable fractionswhich are less suitable for subsequent filtration, can be removed, e.g.,flushed away, upon completion of the fractioning process, by rotation,throughflow and/or back flushing. A suitable fraction or suitablefractions, protects, or protect, the filter cloth or membrane andfacilitates (facilitate) cleaning while reducing contamination with lesssuitable particles and also decrease the apparent average pore size oraverage mesh size in the filter, so as to render subsequent filtrationmore effective i.e. to provide a better filtrate with smaller particleswith regard to both number and size Examples of such less suitableparticles are particles which tend to adhere, which are slimy or tackyand which therefore tend to block the filter cloth or the like and whichmay be difficult to remove when cleaning the filter.

As beforementioned, a multiple of different types of particles can beused. By using filter auxiliaries of elongated form, such as threadform, and by varying the flow directions and flow rates between theconnection 32 and 32', the rotational speeds and rotational directionsof the filter tube 1 etc., it is possible to weave a mat-like layerstructure comprising various layers in which the layers have mutuallydifferent orientation. By utilizing available forces for activation byfractionation and orientation of such filter auxiliaries, it is alsopossible to "equalize" the filter fabric or the like, by blocking largeholes or pores so as to obtain a smaller spread in hole size.

Those forces available are mainly

forces which result from the flow through the filter, i.e. cross-flowfrom the feed inlet 32 to the concentrate outlet 32'.

forces created by rotation of the filter tube 1, i.e. cross-flowperpendicular to the cross-flow mentioned above

forces deriving from a combination from the aforesaid flows caused by,e.g. the impeller 31

centrifugal force created by rotation

forces created as a consequence of the density of the particle inrelation to the liquid in which it is present, i.e. forces which impartto the particle the impulse to sink, hover or rise to the surface

forces resulting from cross-flow when a particle fastens in the filtersurface and accompanies the tube 1 essentially circumferentially of thetube.

It will be apparent from the aforegoing that the present inventionprovides a particularly flexible filtering process while fulfilling theextremely high demands placed in sterility.

Although the invention has been described with reference to embodimentsthereof, it will be understood that other embodiments and minormodifications are conceivable within the scope of the inventive concept.For example, a conceivable embodiment is one in which, by selection,inter alia, of the direction of rotation, the filter cloth, membrane orthe like can be firmly locked to the filter tube, applying overlappingends in the circumferential direction.

Embodiments are also conceivable in which the pressure obtained byscavenging pipes, scavenging plates or the like is utilized forsupplying medium, e.g. the filtrate, to the system used for cooling andlubricating a journalling and sealing unit and in which the pressuredifferential across the seals is measured, in certain instances adjustedaccordingly.

Scavenging pipes or scavenging plates 46 can be arranged within thejournalling or bearing unit according to FIGS. 2 and 3, for pumping outany liquid which might have collected, so as not to subject (ball)bearings to such unsuitable liquids. The scavenging pipe or scavengingplates are preferably placed in the space or chamber 13' or adjacent theball bearings 21'. Discharge is effected via the stationary shaft 13.One embodiment is illustrated in FIG. 10.

As illustrated schematically in FIG. 5, it may be convenient in someinstances to supply clean liquid when sealing in the space 14", thisliquid being mixed with the concentrate by means of the impeller 28, viaan additional seal 28" adjacent the end-cover 3". The clean liquidcleanses and protects the seal, and also facilitates discharge of theconcentrate. Correspondingly, liquid can be admixed with the feedsupplied to the inlet end. This mixture of liquid with the feed or theconcentrate is facilitated by rotation of the filter tube and also bybaffles, impellers, etc., when such devices are present.

Embodiments are also conceivable in which the power consumption ismeasured, there being obtained a measurement of the concentrationachieved, this measurement being used to control the process and toadjust, e.g., the viscosity of the concentrate. One or more impellerscan be used in this case, in order to amplify the measuring signal.

Suitable filter auxiliaries, particles, are often of a nature which willenable them to readily dissolve during a cleaning operation as a resultof changes in temperature, pH or other parameters. Particles which willreadily dissolve in a suitable washing liquor or which can be readilyflushed away may also be chosen.

The permeable filter tube 1 can be arranged in a number of differentways. Thus, the tube may comprise a tubular body, which may be made ofmetal, a plastics material or some other material, and which has aperforated tube wall, or may comprise a tube manufactured from a sintermaterial, such as metal sinter, metal ceramics or the like. According toone preferred embodiment, the tubular body is made of sintered stainlesssteel. The embodiment in which the tubular body is made of sinteredmetal, metal ceramic or ceramic affords important advantages with regardto stability and robustness. Such a filter tube can be cleansed fromparticles deriving from, inter alia, feed, and withstands hightemperatures, chemicals, such as acid, etc. The tubular body ispreferably covered externally with at least one layer of filter net,filter fabric, filter membrane or filter paper. Several such layers maybe placed on the tubular body. According to one embodiment the tubularbody has provided thereon a filter support layer which forms a suitablesupport for a superimposed layer, which also functions as a drainingmaterial so that filtered liquid or backflushing liquid can flowlaterally to suitable holes or suitable pores in the tubular body. Oneor more layers of filter fabric or the like can be placed on thedrainage support layer. Said layer or layers can be coated externallywith additional membranes such as dynamic membranes or precoats offilter auxiliary material or particles taken from the material to befiltered, or a combination of such particles, precoat and/or materialfor constructing a dynamic membrane, e.g. Zr- or Si- compounds oralcohols.

In the aforegoing there has been described an embodiment which comprisesan elastic, direct coupling between motor and drive shaft 6 for thefilter tube. Embodiments are conceivable, however, in which a magneticcoupling, not shown, is provided between drive motor shaft and filtertube or a shaft connected to the filter tube. One advantage affordedhereby is that motor shaft and filter tube or filter shaft can bearranged in spaces which are totally separated from one another. Oneimportant drawback, however, is that relatively long displacementbetween the shafts can only be accepted for short periods of time whenthe transferable torque decreases as respective magnetic parts move fromtheir intended mutual positions.

A channel 22 may, as mentioned, be used for supplying gas, whereby thefiltered liquid in the interior 12 of the tube may be varied bothregarding pressure and quantity.

Changes regarding back pressure, as discussed earlier in connection toback flushing may be performed by means of changes at the filtrateoutlet outside the filter or inside the filter tube 1 via channel 22.

Thus, the invention shall not be considered to be limited to theaforedescribed embodiments, since modifications can be made within thescope of the following claims.

I claim:
 1. A method of operating rotating filters of the kindcomprising a substantially cylindrical filter tube which is providedwith a permeable wall and which is sealingly journalled at at least onelocations, for rotation about its longitudinal axis in a filter jacket,in which method feed material to be filtered is supplied to a spacelocated between the filter jacket and the filter tube, and in whichfiltered material, the filtrate, can be tapped from the interior of thefilter tube, characterized by the step of sealing and journalling thefilter tube (1) in a manner adapted to substantial temperature changesof the filter tube, seals and bearings being adapted to take up axialdisplacement movements and forces resulting essentially from changes inthe temperature of the filter tube, by means of a journalling andsealing unit attached to the filter tube (1) and arranged adjacent atleast one end (1') of the filter tube, said unit comprising twosubstantially cylindrical parts (15', 16'), one external (15') and oneinternal (16'), which are co-acting in a sealed and axially displaceablerelationship.
 2. A method of operating rotating filters as defined inclaim 1, including the further step of sterilizing and lubricating andcooling the bearings and seals with aid of sterilizing media.
 3. Amethod as defined in claim 1 wherein sealing and journalling the filtertube is undertaken at two axially spaced-apart filter tube locations. 4.A method according to claim 1, characterized by the further step ofutilizing the rotational movement for discharging filtrate with the aidof a scavenging means (24,35), it being possible to adjust saiddischarge by said scavenging means.
 5. A method according to claim 1,characterized by utilizing rotational movement of the filter tube forgenerating, by means of an impeller (19,28,31), pressure intended forfeeding, pressure relieving, circulating, cross-flow and discharging ofconcentrate.
 6. A method according to claim 5, characterized bygenerating pressure for at least partially relieving pressure on seals(9, 14, 20) located adjacent a bearing.
 7. A method according to claim5, characterized by generating pressure for the discharge ofconcentrate, and wherein the filter jacket (2) has a conical shape forfacilitating said discharge, and said rotary movement being used alsofor feeding concentrate mechanically by means of discharge vanes bothpast the surface of the filter tube (1) and out of the filter unit.
 8. Amethod according to claim 1, characterized by utilizing scavenger means(24) for varying the amount of filtrate in the filter a shaft, aboutwhich filter tube rotation takes place, being eccentrically locatedrelative to a part of said scavenging means, the filter tube opening(20) being capable of taking different radial positions in the filtertube (1).
 9. A method according to claim 1, characterized by utilizingscavenger means (24) for varying the amount of backflushing liquidavailable, a shaft, about which filter tube rotation takes place beingeccentrically located relative to the scavenging means, the filter tubeopening (20) being capable of taking different radial positions in thefilter tube (1).
 10. A method according to claim 1, characterized inthat washing and cleansing are effected by backflushing, liquid beingsupplied from within the filter tube (1) in the filter through ascavenger pipe.
 11. A method according to claim 1, characterized in thatwashing and cleansing are effected by backflushing liquid being suppliedfrom within the filter tube (1) in the filter through a scavenger plate.12. A method according to claim 1, characterized in that washing andcleansing are effected by backflushing, liquid being supplied fromwithin the filter tube (1) in the filter through a separate flushingpipe.
 13. A method according to claim 1, characterized in that washingand cleansing are effected by backflushing, liquid being supplied fromwithin the filter tube (1) in the filter through the filter tube (1)because of rotation.
 14. A method according to claim 1, characterized inthat backflushing is effected by varying the pressure conditions.
 15. Amethod as defined in claim 14, wherein the variation of pressureconditions is accomplished by varying the volume ratio.
 16. A method asdefined in claim 14, wherein the variation of pressure conditions isaccomplished by variation of speed of filter tube rotation.
 17. A methodaccording to claim 1, characterized by utilizing rotational movement incombination with the flow from the inlet (32) to the outlet (32') ofmaterial to be filtered in the space between the filter tube and thefilter jacket, the flow in the circumferential direction of the filtertube (1) resulting from said rotation, backflushing and particledensity.
 18. A filter of the rotating kind comprising a substantiallycylindrical filter jacket, a substantially cylindrical filter tube whichhas a permeable wall and which is sealingly journalled by seals andbearings at least one axial locations, for rotation about itslongitudinal axis in said filter jacket, the material to be filtered,the feed, being supplied to a first space located at one end of andbetween the filter jacket and the filter tube, and the filteredmaterial, the filtrate, being tapped from the interior of the filtertube, and wherein the seals (9, 14, 20, 21) and bearings of the filtertube (1) are sterilizably arranged and constructed so as to take upaxial displacement movements and forces resulting essentially fromchanges in the temperature of the filter tube (1), seals and bearingscomprising means including a journalling and sealing unit attached tosaid filter tube (1) and arranged adjacent said one end (1') of saidfilter tube (1), said unit comprising two substantially cylindricalparts (15', 16'), one external (15') and one internal (16'), which arearranged to co-act in a sealed and axially displaceable relationship,and wherein said seals (9, 14, 20, 21) and bearings are constructed toenable said seals and bearings to be sterilized and lubricated andcooled by means of a sterilizing media.
 19. A filter according to claim18, characterized in that said filter includes a non-rotatable shaft,said filter tube is sealingly journalled at both tube ends on said shaftand said filter tube is journalled at one said end (1') for axialdisplacement on said non-rotatable shaft (13), while maintaining thesealing function.
 20. A filter as defined in claim 19, wherein saidfilter jacket has an end-cover part (3") and said shaft is carried bysaid end-cover part.
 21. A filter according to claim 19, characterizedin that said journalling and sealing unit comprises a first part (15),which is sealingly journalled at said shaft (13) and includes saidexternal, substantially cylindrical part (15') and further comprises asecond part (16), which is connected to the first tube (1) and, whenseen in the direction of the tube radius, is located essentially betweenthe filter tube and said first cylindrical part (15), and wherein saidexternal second part includes said internal, substantially cylindricalpart (16'), said end of the filter tube being sealingly fitted to saidnon-rotatable shaft (13).
 22. A filter according to claim 19,characterized in that said non-rotatable shaft (13) is provided with atleast one axially extending channel (22), arranged to connect theinterior (12) of the filter tube with the outside of the filter jacket(2).
 23. A filter according to claim 19, characterized in that a pumpimpeller (28) is arranged at the filter tube end (1') journalled forrelative axial displacement, and can be rotated about said shaft by thetube, and wherein the impeller is arranged to lower the pressure atseveral parts for the purpose of relieving pressure adjacent thejournalling and sealing unit in the filter jacket (2).
 24. A filteraccording to claim 23, characterized in that said impeller (28) isprovided with vanes (29) for feeding material axially in said filterjacket (2).
 25. A filter according to claim 19, characterized in that apump impeller (31) is arranged in the filter jacket (2) adjacent aninlet (32) for the material to be filtered; and in that said impeller(31) is provided to increase the pressure at said inlet and to at leastpartially relieve the pressure in connection with said journalling andsealing unit in the filter jacket (2) adjacent said inlet.
 26. A filteraccording to claim 18, characterized in that the journalling and sealingunit includes sealing parts which are mechanically displaceable in theaxial direction and thereby are arranged to take up at least parts ofsaid axial displacement.
 27. A filter according to claim 18,characterized in that a scavenger means (24) is provided in the filtertube (1) for discharging filtrate from said tube, while utilizing therotational movement of said tube; and wherein said scavenger means iseffective in adjusting the discharge of filtrate.
 28. A filter accordingto claim 27, characterized in that discharge by means of said scavengermeans (24) is controllable by said scavenger means which includes afirst part (24'), extending essentially parallel with the longitudinalaxis of the filter tube (1), and a second part (24") which extends atleast partially in the direction of the filter tube radius and which isconnected to the first mentioned part (24'), and the free end (25) ofsaid second part (24") includes a substantially tangential filtrateinlet (26) of said scavenger means, and wherein said scavenger meansfirst part is located eccentrically in the filter tube so that theprevailing radial position of the filtrate inlet in the filter tube atsaid free end of said second part can be adjusted by pivoting theradially extending second part (24") about an eccentrically locatedaxially extending plane.
 29. A filter as defined in claim 28, whereinthe prevailing radial position of the filtrate inlet in the filter tubeat said free end of said second part is adjusted by pivoting theradially extending part (24") about the longitudinal axis of said firstpart.
 30. A filter according to claim 27 characterized in that inaddition to the filtrate tapping pipe (22), which connects the interior(12) of the filter tube with the outside of the filter jacket, there isprovided a flushing pipe (22) through which a fluid material is suppliedto the filter tube, and in that said connections between the filter tubeand the outside of the filter jacket extend, via and include a fixedshaft (13) on which one end (1) of the filter tube is sealinglyjournalled.
 31. A filter according to claim 27, characterized in thatsaid scavenger means for discharging filtrate from the filter tube isadjustably arranged thereby enabling control of the amount of filtratein the filter tube.
 32. A filter according to claim 18, characterized inthat a baffle device is provided to increase turbulence in the firstspace (11) located between said filter tube (1) and said filter jacket(2), said baffle device being mounted in the first space between thefilter tube and the filter jacket to create said increased turbulenceand making the radial distance between the filter tube and the filterjacket effectively smaller.
 33. A filter according to claim 18,characterized in that a second space (36) is arranged in the filter tubeat a location adjacent the other end of the filter tube, said filtertube being intended for use with its longitudinal axis extendingessentially vertically so that said other end is the lower end, saidsecond space (36) being the last space to be rendered dry when emptyingthe filter tube; in that scavenger means is a pipe (35) and the inletopening (35) of the scavenger pipe (35) is located in the bottom part ofsaid second space (36) in order to enable the filter tube to be broughtto an essentially dry state; in that the inlet outlet opening of saidscavenger pipe is of small dimensions; and in that the inlet opening ofsaid scavenger pipe is connected to a pipe of larger dimensions.
 34. Afilter according to claim 18, characterized in that the filter jacket(2) has a substantially conical configuration and widens out towards theoutlet end, so as to facilitate the discharge sludge.
 35. A filteraccording to claim 18, characterized in that the body of said filtertube (1) is made from a sintered material.
 36. A filter as defined inclaim 35, wherein said filter tube is made from sintered stainlesssteel.